During frying, fat is exposed to elevated temperatures and atmospheric oxygen, resulting in deterioration in flavor, color, and nutritive value of the oil, especially reductions in essential fatty acids. The main changes occurring during frying include oxidation, hydrolysis, and polymerization.
Oxidation can be retarded by adding antioxidants, but most phenolic antioxidants undergo distillation or destruction in deep-fat frying conditions, thus, minimizing their protective effect under these conditions. The commonly used synthetic autoxidation inhibitor for frying oil is poly(dimethylsiloxane) (MS) (Gordon, “The Mechanism of the Antioxidant Action in Vitro, in Hudson, ed., Food Antioxidant, Elsevier, pp. 13-14 (1990)). (The term “autoxidation inhibitor” refers to substances that inhibit autoxidation, when added to fats and oils at low concentrations and whose mechanism of action may be unknown. Such substances are commonly referred to as “antioxidants,” but some use the term “antioxidants” only for substances that end free radical chains by hydrogen radical donation.) MS was originally used in frying oils to prevent foaming, and its mechanism for retarding oxidation is uncertain. One hypothesis is that it accumulates in the oil surface and acts an oxygen barrier. Disadvantages of using MS are: loss of volume in cake baking, batter defoaming in doughnut frying, and loss of crispness in fried potato chips (Frankel, Lipid Oxidation, pp. 244-245 Oily Press Ltd., Dundee, Scotland (1998)).
Many people prefer to have “natural” autoxidation inhibitors in their food, but so far there has not been a natural frying autoxidation inhibitor that is effective and available. A number of plant sterols, including Δ5- and Δ7-avenasterol, vernosterol, and citrostadienol (see FIG. 1) reduce the chemical changes that occur in vegetable oils during frying (Gordon and Magos, “The Effect of Sterols on the Oxidation of Edible Oils,” Food Chem., 10:141-147 (1983); White and Armstrong, “Effect of Selected Oat Sterols on the Deterioration of Heated Soybean Oil,” J. Am. Oil Chem. Soc., 6:525-529 (1986)). Gordon and Magos (Gordon and Magos, “The Effect of Sterols on the Oxidation of Edible Oils,” Food Chem., 10:141-147 (1983)) theorized that the ethylidine side chain present on these sterols reacts rapidly with lipid free radicals to form “stable” allylic tertiary free radicals that are too weak to continue the oxidation chain. The ethylidene side chain forms free radicals rapidly, because of the presence of unhindered hydrogen atoms on an allylic carbon atom.
Linalool (see FIG. 1), a terpenol compound found in herbs, such as basil and coriander, contains a double bond structure similar to that found in the plant sterols, and has a prooxidative effect in frying oil when present above 0.05% (Yan and White, “Linalyl Acetate and Other Compounds with Related Structures as Antioxidants in Heated Soybean Oil,” J. Agric. Food Chem., 38:1904-1908 (1990)). But this prooxidative effect can be avoided by esterification of linalool's hydroxyl group, for instance with linalool acetate (LA; see FIG. 1). The disadvantages of LA are that it possesses a relatively strong flavor and tends to distill out of the fat at frying temperature.
The present invention is directed to overcoming these deficiencies in the art.